The Tissue Bank (Core C) provides the infrastructure to provide specimens from patients with myeloproliferative neoplasms (MPN) to investigators performing translational research for the purpose of developing innovative therapies for MPN pafients. The functions of the tissue bank are to: 1) acquire MPN tissues, 2) act as a repository for MPN tissues, 3) distribute MPN fissues for research, and 4) facilitate the performance of biomarker assays by distributing tissues to core laboratories. Tissues are available to members of the MPD Research Consortium (MPD-RC) and to the scientific community at large for the performance of translational research. Core C is an essential shared resource that enables translational research that will result in improved diagnosis and staging of MPN and ultimately lead to the development of molecularly targeted therapies. The specific aims of Tissue Bank Core C are to: 1) Receive, process, cryopreserve, and store tissues from MPN patients diagnosed at MPD-RC clinical sites in an efficient, organized manner according to standard operafing procedures (SOPs). 2) Provide a central repository for MPN tissues that are associated with basic data stored in the web-based data bank maintained by Biostatistics and Data Management Core B. These basic data include clinical, laboratory and familial demographic data that enable selection and distribution of tissues best suited for each translational research project. 3) Make the cryopreseved tissues readily available to the MPD Consortium investigators and scientific community at large for research studies. 4) Facilitate the performance of biomarker assays designed to predict disease progression, thrombofic complications, and therapeutic response, by receiving, processing, cryopreserving, and storing tissues from MPN patients, and distributing these tissues to consortium biomarker assay labs. These tissues are collected from patients at diagnosis and at intervals designated in individual protocols described in Project 6. Biomarker assays provide data that are anticipated to correlate with clinical trial endpoints. Specimens from more than 600 patients are cun-ently banked in Core C. Tissues from more than 275 patients have been distributed for research to members of the MPD-RC and the scientific community at large.